Death Valley geology field trip

Split Cindercone

Aerial view of Split Cinder Cone. Photo by Tom Bean, NPS.

You'll remember that the basaltic lava that built Split Cinder Cone used rock weakened by a branch of the Death Valley Fault zone. Split Cinder Cone was probably built over a very short time; its birth and death probably spanned less than a few decades.
Although the little volcano lay quiet, the Death Valley Fault zone continued to move as it had for almost three million years. The wrenching force of this very active fault pulled one part of the volcano to the southeast, while the other part was pulled toward the northwest.
Eventually, the crust could no longer resist the wrenching motion of the fault and the cinder cone began to be ripped into two pieces. Each time the fault moved, the two sides of the cone moved farther apart.

Arrows indicate the direction of movement. Dotted line shows approximate location of the fault that created Split Cinder Cone. Photo by Tom Bean, NPS.

This type of side-by-side fault movement is referred to as strike-slip. Because one side of the cinder cone is being moved to the right, relative to the other side, this fault is a right-lateral strike slip fault. The upper part of the once symmetrical cone has been moved to the right 300 feet (91 meters) relative to the lower part.
Features like Split Cinder Cone can be used to determine the rate of movement along the Death Valley Fault zone. The volcanic rock from which the cinder cone is made can be radiometrically dated. Once geologists know the age of a feature cut by a fault, and the distance the two parts have moved apart, the rate of movement on each branch of the fault can be estimated.